The distribution of a secret key is probably the main Achilles' heel of many secure communication system. To establish a completely secure information transfer it is necessary for two users to share a secret key, known only to them, before the communication can take place. In many practical scenarios, especially when the two users are separated by a large distance, this requirement is difficult to realize because secure transmission of the key requires a previously shared (additional) key.
This loophole was one of the main incentives behind the attempts to develop physically (as opposed to algorithmically) secure key distribution schemes, based on the fundamental properties of quantum mechanics. Although ideally such communication protocols are perfectly secured, their practical implementation is not simple. Noise and attenuation in the quantum channel significantly reduce their efficiency, especially from the range and data rate aspects. Theoretical and experimental studies show that channel attenuation, noise and detector dark-counts limit the key-establishing rates and the operational ranges of Quantum Key Distribution (QKD) systems.
Various prior art QKD systems, as well as some of the problems associated with QKD systems are illustrated in the following cited articles, patents and patent applications, provide a general background of the prior art: C. H. Bennett and G. Brassard, “Quantum cryptography: Public key distribution and coin tossing”, International Conference on Computers, Systems & Signal Processing, Bangalore, India, December 10-12, pp 175-179 (1984); N. Gisin, G. Ribordy, W. Tittel and Zbinden, “Quantum cryptography”, Rev. Mod. Phys. 74, pp. 145-195 (2002); A. Ekert, “Beating the code breakers”, Nature 358, pp. 14-15 (1992); E. Waks, K. Inoue, C. Santori, D. Fattal, J. Vuckovic, G. S. Solomon, and Y. Yamamoto, “Quantum cryptography with a photon turnstile”, Nature 420, p. 762 (2002); L.-M. Duan, M. D. Lukin, J. I. Cirac and P. Zoller, “Long-distance quantum communication with atomic ensembles and linear optics”, Nature 414, pp. 413-418 (2001); M. Aspelmeyer, H. R. Bohm, T. Gyatso, T. Jennewein, R. Kaltenbaek, M. Lindenthal, G. M Terriza, A. Poppe, K. Resch, M. Taraba, R. Ursin, P. Walther, and A. Zeilinger, “Long-Distance Free-Space Distribution of Quantum Entanglement” Science 301, pp. 621-623 (2003); I. Marcikic, H. de Reidmatten, W. Tittel, H. Zbinden, M. Legre, and N. Gisin, “Distribution of Time-Bin Entangled Qubits over 50 km of Optical Fiber”, Phys. Rev. Lett. 93, p. 180502 (2004); R. J. Hughes, G. L. Morgan and C. G. Peterson, “Quantum key distribution over a 48 km optical fiber network”, J. Mod. Opt. 47, pp. 533-547 (2000); C. Gobby, Z. L. Yual and A. J. Shields, “Quantum key distribution over 122 km of standard telecom fiber”, Appl. Phys. Lett. 84, pp. 3762-3764 (2004);U.S. Pat. No. 6,529,601 of Towsend; U.S. Pat. No. 6,748,081 of Dultz et al; U.S. Pat. No. 7,068,790 of Eliott; U.S patent application 2004/032954 of Bonfarte; U.S patent application 2006/193636 of Katagitie; US patent application 2006/239463 of Young; and PCT patent application WO/0697966 of Cortese.
Recently, a classical Key Distribution System (KDS) utilizing Johnson noise in resistors was suggested. Although conceptually interesting, the suggested scheme was found to be vulnerable to an analysis of the transients of the electromagnetic waves propagating in the transmission line connecting the two parties. Such prior art KDS systems as well as some of the problems associated with these KDS systems are illustrated in the following articles, and provide a general background of the prior art: L. B. Kish, “Totally secure classical communication utilizing Johnson (-like) noise and Kirchoff's law”, pla15171, in press, doi:10.1016/j.physleta.2005.11.062; A. Cho, “Simple Noise May Stymie Spies Without Quantum Weirdness”, Science 309, p. 2148 (2005); J. Scheuer and A. Yariv, “A Classical Key-Distribution System based on Johnson (like) noise—How Secure?”, arXiv: physics/0601022 v3, 8 Jan. 2006; and P. W. Shor and J. Preskill, “Simple proof of security of the BB84 quantum key distribution protocol”, Phys. Rev. Lett. 85, pp 441-444 (2000).
There is a need to provide highly secured communication systems and methods.